Men with intermediate or high risk prostate cancer who are technically suitable for prostate brachytherapy based on prostate size and voiding function and who are interested in this modality of treatment will be approached for randomization between either high dose rate (single 15 Gray) or low dose rate permanent seed implant (110 Gray) brachytherapy. Baseline International Prostate Symptom score, Quality of Life Assessment and International Index of Erectile Function will be recorded and then every 3 months for the first year and every 6 months to 3 years. Androgen deprivation treatment is allowed for 6 or 12 months.